Integrated circuit (IC) devices are manufactured by forming layered metallic circuit components and patterns on a semiconductor wafer. Numerous IC die are formed on a single wafer. The individual IC die on the wafer are separated from one another by a singulation process, such as sawing. Each IC die is typically mounted on a metallic leadframe, and the IC-leadframe assembly is then encapsulated within a package. Packaging material, or “encapsulant” is commonly made from viscous or semi-viscous plastic or epoxy resin, which is cured to form a hardened protective cover to protect the IC assembly from environmental hazards such as dust, heat, moisture, mechanical shock, and external electricity.
IC packaging is conventionally accomplished using a molding process. The specifics of the molding process are influenced by many factors such as the IC and leadframe geometry, and encapsulant material used, but generally proceeds along the lines of one of the most widely used manufacturing processes, known as transfer molding.
In conventional transfer molding a pellet load operation is performed by pellet loading apparatus including a pellet dispenser that has a plurality of stacks of mold compound solid pellets that are between adjacent vertical members known as magazines and a tablet lifter section comprising a pellet stopper having a plurality of pellet receiving positions. The pellet dispenser includes a tablet pusher which applies a spring force in the vertical direction. The spring force is intended to transfer only the top pellets in each pellet stack at each transfer time into the receiving positions of the pellet stopper. The tablet lifter then transfers the pellets received into a mold of a molding section that holds IC-leadframe assemblies in molding cavities, where the mold compound is melted by the application of heat and pressure to a fluid state. The liquefied mold compound is then forced by a plunger into runners connected between the plunger and molding cavities to encapsulate the IC-leadframe assemblies, followed by cooling and removal from the molding cavities.
One problem with transfer molding occurs when more than one pellet (typically two pellets) is transferred (resulting in double pellet transfer) into respective mold cavities in the mold section from the pellet stopper during pellet transfer. A known solution to double pellet transfer is to stop the molding machine to allow removal of the extra pellets from the pellet stopper, then reinitializing the molding machine. Although this known solution is effective in clearing the problem, the clearing process results in system downtime and results in the loss of productivity.